This three-year study will target male couples of known serodiscordant- HIV status. Half of these couples will have at least one Puerto Rican member. The primary goal of this study is to assess the contextual and psychological (affective, cognitive and behavioral) determinants of sexual-risk behavior. The secondary goal is to develop a theory-driven intervention to reduce high-risk sexual behavior. The specific objectives of this study are: 1) to develop or to adapt quantitative assessment instruments to measure the couples' sexual-risk behavior and its determinants; the units of assessment will be both the couple and the individual; 2) to assess the sexual-risk behavior or 80 couples and its determinants; 3) to conduct exploratory analyses and test specific hypotheses related to determinants of high-risk sex behavior, guided by the theoretically based Modified AIDS Risk Reduction Model (MARRM); and finally, 4) to develop and pilot test a behavioral intervention based on a version of the MARRM adapted for male couples. Data collection will utilize both qualitative and quantitative techniques. Qualitative elicitation will identify determinants of sexual risk behavior in couples, inform the development of the assessment tools and the intervention. The cross-sectional determinant study will apply quantitative statistical techniques to explore relationships between contextual, psychological, and relationship variables with sexual risk behavior in the couple. Specific stage and mediating variables of the MARRM will be tested and the model will be subsequently modified for this population. An intervention will then be developed and piloted. Results of this study will not only lead to the development of a model intervention for serodiscordant male couples, but will also inform the development of determinant studies and interventions for other types of couples (i.e., serodiscordant heterosexual couples and lesbian couples, couples where both members are HIV seropositive, and seronegative couples at risk).